Results of the Habitat Risk Assessment Cumulative risk scores ranged from 0 to 10.7, out of a possible maximum cumulative risk score of 21. Credit: Rudebusch et al. 2020
Human activity could undermine the success of efforts to reintroduce sea otters to San Francisco Bay.
Although past studies have found that the Bay could support 1.5 times the entire current southern sea otter population, a new study from the Estuary & Ocean Science Center at San Francisco State University and published by PeerJ
last November indicates that anthropogenic risks like contaminants, vessel traffic, and oil spills may constrain the otter’s ability to gain a foothold. The study, led by Jane Rudebusch, at the time graduate student at SFSU, looked at the types of human stressors present and ranked them according to factors like temporal overlap (frequency of its interaction with otters), intensity (consequence of that interaction), and management effectiveness (how well the stressor is mitigated by human regulation). The study concluded that high-speed vessel traffic, such as commuter ferries, was of primary concern. However, Rudebusch found that “the risk from human disturbance is really not evenly spread throughout the Bay. You can look at pockets of the Bay where there is lower risk and use those to focus a reintroduction effort.” Sites like China Camp on the Marin bayshore are particularly appealing because of their protected status and relative lack of human stressors. Rudebusch says it was important to capture a picture of the entire area because “although sea otters occupy a small home range, they can also travel great distances. Where you put them is not necessarily where they are going to stay.” San Francisco Bay presents an interesting reintroduction site because of the success of the population at Elkhorn Slough—another estuarine habitat in Monterey Bay—and otters’ inability to naturally expand their range north of Pigeon Point, where they are prey for great white sharks. Returning otters to their original pan-California range would improve the health of the coastline and estuaries. “Sea otters are a keystone species, this singular glue that holds an ecosystem together,” says Rudebusch. “For over a hundred years, [many] ecosystems in California have been missing this key link.”